1. Field of the Invention
The present invention pertains to exhaust systems for water craft, and more particularly to improved marine wet exhaust systems for reducing the emission of particulate materials in the exhaust flows of marine engines.
2. Description of the Related Art
The internal combustion engines commonly used to power watercraft generate power through the rapid combustion of organic fuels and the expansion of the combustion products against pistons coupled to a drive shaft. The combustion products typically include particulate materials capable of polluting the surrounding air or water when released. The periodic combustion, expansion and discharge of the combustion products also produces undesirable heat and noise in the exhaust flow from the engine.
Internal combustion engines utilized in watercraft typically use the water supporting the craft for cooling purposes. The water is drawn into the craft and circulated through an engine cooling jacket or engine coolant heat exchanger. The water is then commonly injected into the exhaust system to cool the combustion products so that they might be safely discharged through the hull of the craft without presenting a fire hazard. Accordingly, a marine wet exhaust system must handle not only exhaust gases, but also the waste cooling fluid or water which is injected into the exhaust system.
In addition to safely handling exhaust gases and waste cooling water, a marine wet exhaust system should muffle or attenuate the exhaust noise generated by operation of the marine engine. Muffling of exhaust noise from marine engines has been handled in a number of ways. For example, the exhaust may be discharged below the water level. In outboard engines and in inboard/outdrive installations the exhaust is sometimes routed through the drive unit so that the exhaust gas and waste cooling water are discharged through or adjacent the propeller driving the craft. An exhaust system including a water separator for use in outboard drive units with exhaust routed through the propeller under the water line is disclosed in North et al., U.S. Pat. No. 3,759,041.
Mufflers are often placed along the exhaust conduit running between the engine and the exhaust discharge to attenuate the exhaust noise. One such example is shown in Harbert, U.S. Pat. No. 5,022,877.
Often, marine muffler designs are closely akin to the mufflers used on automobiles, but are constructed of materials such as fiberglass which can better tolerate the marine environment. While such mufflers are popular in the boating industry, many do not provide good attenuation of the noise generated by marine engines.
Furthermore, such mufflers often do not adequately separate water from the exhaust gas, even if they are designed to perform any water separation at all. The engine and muffler are often mounted amidship and located as far as 30 ft. to 40 ft. from the discharge. At these lengths it is difficult to maintain an overall downward grade necessary to drain the waste coolant water separated from the exhaust flow. In practice, the exhaust conduit leading from the muffler to the discharge may curl up-and-down as it crosses various sections of the boat, creating traps where water may accumulate and constrict the exhaust flow.
Even among those devices which do separate cooling water from the exhaust flow, it does not appear that any provision has been made to separate particulate materials from either the cooling water or the exhaust flow before the cooling water and exhaust are discharged into the surrounding water and the atmosphere.
Catalytic converters have been used in land vehicles to adsorb or otherwise remove pollutants from automotive exhaust flows. Such devices are less practical in marine craft, however, inasmuch as the very high temperatures necessary to the reduction processes in the converters cannot be tolerated in the less efficiently ventilated engine spaces in water craft.
Consequently, there remains a need for a marine wet exhaust system capable of both attenuating exhaust noise and separating particulate material before the cooling water and the exhaust are discharged.